WASHINGTON — When Alonzo J. King, Jr. was arrested for threatening a group of people with a shotgun in Wicomico County, Md., he quickly pled guilty and was convicted of second-degree assault. However, what transpired during his arrest has brought his case to the Supreme Court and put DNA collection under the microscope.

The Court heard oral arguments for what Justice Samuel Alito called “perhaps the most important criminal procedure case that this Court has heard in decades” in Maryland v. King. At the case’s core was the constitutionality of states collecting and analyzing DNA from people arrested, but not convicted, of serious crimes.

“We’re talking about a special class of people,” said Katherine Winfree, the Maryland deputy attorney general. “They are lawfully in custody based upon probable cause.”

In April 2009, King was arrested and charged with first and second degree felony assault after threatening a group of people with a shotgun. Police collected skin cells from inside King’s mouth for DNA testing, pursuant to Maryland law. After being matched to an unsolved sexual assault case, King was convicted and sentenced to life in prison.

Believing his Fourth Amendment privilege against warrantless searches had been violated, King appealed. The Maryland Court of Appeals reversed the conviction, holding that the law was unconstitutional because King’s expectation of privacy was greater than Maryland’s interest in using the DNA for identification purposes.

U.S. Deputy Solicitor General Michael Dreeben, who appeared in support of Maryland’s position, claimed that since arrested individuals are subject to different expectations of privacy, such as being strip searched, and have often been previously arrested, a simple cotton swab to collect DNA should not be out of the question.

He said taking a DNA sample from a suspect in custody is much less intrusive than going into someone’s house, which would “expose a substantial number of highly private things to the view of the state.

That comparison of DNA collection and fingerprinting fueled much of the debate Tuesday morning.

“[DNA collection] is the fingerprinting of the 21st century, but it’s better,” Winfree said. “Typically DNA evidence is used to identify rapes and murderers. Fingerprints typically do not solve those kinds of crimes.”

DNA analysis has become a common practice for law enforcement across the country. A majority of states have passed laws that allow police to collect DNA from suspects to be tested for matches for unsolved crimes in criminal databases, including the FBI’s.

“The state has a compelling interest in taking biometric identification information from the individual that is arrested and using it for a myriad of purposes,” Dreeben said, including determining their criminal history and attempting to solve unsolved crimes.

King’s lawyer, Kannon Shanmugam, disagreed, saying fingerprinting is mainly to identify a suspect while DNA testing goes much further.

“…[T]he primary purpose of DNA testing, unlike fingerprinting, is to investigate unsolved crimes,” said Shanmugam, responding to Justice Anthony Kennedy’s question regarding the law’s right to know a suspect’s previous criminal record.

Many of the justices were apprehensive about allowing DNA collection without a warrant for individuals only suspected and not charged with a crime.

“The purpose now is…to catch the bad guys, which is a good thing,” Justice Antonin Scalia said. “But you know, the Fourth Amendment sometimes stands in the way.”

Previously, courts have overwhelmingly sided with the federal and state governments when it comes to DNA collection from convicted criminals. However technology once again has members of the High Court nervous about passing a broad precedent that could alter the way the law is enforced.

“There is something inherently dangerous about DNA collection that is not the same as fingerprinting,” said Justice Sonia Sotomayor.

Chief Justice John Roberts was concerned that the law may be moving faster than technology.

“You’re not going to put off the bail hearing for two weeks,” Roberts said, to see if there is a DNA match.

The Court is expected to deliver its opinion on Maryland v. King early this summer.